1. Field of Invention
This invention relates to a method for forming quarter-pitch patterns.
2. Description of Related Art
The resolution in a photolithography process depends on the wavelength of the exposure light, the numerical aperture (NA) of the optical system and the design of the photomask. When the resolution needed by an array of patterns exceeds the resolution of the lithographic system, e.g., in a case of forming the gate line array of a high-density memory like a DRAM of next generation, a pitch reduction method is needed, mainly based on the spacer forming technique.
For example, patterns of conductor lines beyond lithographic resolution can be formed as follows. Base line patterns are lithographically defined and trimmed, linear spacers having a half pitch and a double number are formed on the sidewalls of the base line patterns, and then the base line patterns are removed, leaving the linear spacers as half-pitch line patterns beyond the lithographic resolution.
However, the requirement of increasing the memory density never stops.